1. Field of the Invention
The present invention relates to a method of manufacturing a waved disk for a friction engaging apparatus which is used as a speed-change clutch, a brake or the like in an automatic transmission for a vehicle such as a motor vehicle.
2. Description of Related Art
A friction engaging apparatus is provided with externally toothed disks (i.e., disks which have teeth along an outer edge or circumference thereof) which are engaged with an outer member by means of a spline structure, and internally toothed disks (i.e., disks which have teeth along an inner edge thereof) which are engaged with an inner member by means of a spline structure. The externally toothed disks and the internally toothed disks are brought into urging or pressing contact with each other in a direction of the thickness of the disks to effect a frictional engagement. A torque can thus be transmitted between the outer disks and the inner disks.
Conventionally, in this kind of friction engaging apparatus, there is known one in which either the externally toothed disks or the internally toothed disks are constituted by waved disks which are waved or undulated into a wave shape in the direction of the disk thickness with a circumferential direction being defined as the direction of a wave length (see Published Unexamined Japanese Patent Application No. 257058/1997).
When the above-described kind of waved disks are used, there can be obtained the following features. Namely, at the initial time of engagement, the waved disks are brought into urging contact with the remaining disks (i.e., non-waved disks) while mountains and valleys in wave shape of the waved disks are elastically deformed. Due to buffering or shock absorbing function as a result of the elastic deformation of the mountains and the valleys, a sudden rise or increase in the torque at the initial time of the engagement can be prevented. The shocks at the time of engagement can thus be alleviated. In addition, at the time of disengagement, the waved disks are rapidly departed from the remaining disks (i.e., non-waved disks) due to restoring forces of the mountains and the valleys. Dragging or dragged engagement of the disks can thus be restrained.
As a method of manufacturing this kind of waved disks, there has hitherto been known the following method. Namely, there is used a pressing apparatus which is made up of a stationary die and a movable die. The stationary die has formed therein a plurality of pressing portions which are radially provided in a manner to rise from the surface of the die so as to correspond to ridges of either the mountains or the valleys in the wave of the waved disks. The movable die has formed therein a plurality of pressing portions which are radially provided in a manner to rise from the surface of the die so as to correspond to ridges of either the valleys and the mountains in the wave of the waved disks. A disk blank (a disk raw material) which is made up of an annular flat plate having a toothed portion along its outer edge or circumference or along its inner edge is pressed in the direction of the plate thickness between the stationary die and the movable die, whereby the waved disk is formed by pressing.
At the time of pressing the waved disk as described above, the disk blank is conventionally set in position in an arbitrary phase relationship with the stationary die. As a result, the pressing portions of the stationary die or the movable die happen to coincide with the toothed portions of the disk blank. Ridges (i.e., highest portions or lowest portions) of the mountains and valleys in the wave are thus formed to be elongated up to the toothed portions, too. Here, in those mountains or valleys which have the ridges elongated up to the toothed portions, the forming or pressing load becomes large. If the press forming is carried out by controlling the load of the movable die, the wave height becomes small, resulting in deviations in the wave height from waved disk to waved disk. If, on the other hand, the press forming is carried out by controlling the stroke of the movable die, the wave height will not deviate. However, the rigidity against deformation in the direction of the thickness of the plate becomes high in those mountains and valleys which have the ridges elongated up to the toothed portion. Therefore, the load characteristics vary from waved disk to waved disk. As a consequence, due to deviations in the wave height as well as in the load characteristics, there will occur deviations also in the characteristics of alleviating the engaging shocks and in the characteristics of preventing the dragging.
In view of the above points, the present invention has an object of providing a method of manufacturing a waved disk which is uniform in the wave height as well as in the load characteristics.
In order to attain the above and other objects, the present invention is a method of manufacturing a waved disk which is used as a disk for a friction engaging apparatus, the waved disk having a toothed portion along one of an outer edge and an inner edge of the waved disk, the waved disk being bent into a wave shape in a direction of a thickness of the waved disk with a circumferential direction being defined as a direction of a wave length. The method is carried out with a pressing apparatus comprising a stationary die and a movable die, the stationary die having a plurality of pressing portions radially provided in a manner raised from a surface of the stationary die so as to correspond to ridges of one of mountains and valleys of the wave shape, the movable die having a plurality of pressing portions radially provided in a manner raised from a surface of the movable die so as to correspond to ridges of the other of the mountains and valleys of the wave shape. The method comprises pressing, between the stationary die and the movable die, a disk blank made up of an annular flat plate having a toothed portion along one of the outer edge and the inner edge to thereby form a wave disk by pressing, wherein the pressing is carried out in a state in which the toothed portion of the disk blank is positioned in such a phase as to be circumferentially away from each of the pressing portions of the stationary die and of the movable die.
According to the present invention, the mountains and valleys of the wave are formed by pressing so as to be present in a position circumferentially away from the toothed portion. Therefore, even if the press forming is carried out in either the load control or the stroke control of the movable die, there can be obtained a waved disk which is uniform in both the wave height and the load characteristics.